Determination of the Valence State of Diruthenium Moiety Using Redox Reactions and Surface-Enhanced Raman Scattering: Application in Heterometal Extended Metal-Atom Chain Diruthenium Nickel Complexes

Redox reaction was photoinduced on metal nanoparticle (NP) with diruthenium complexes absorbing on the surface. Surface enhanced Raman scattering (SERS) was employed to detect the vibrational wavenumber of the Ru–Ru stretching mode νRu–Ru,str. During reaction, the local environment remains roughly unaltered; the variation of bonding strength of Ru–Ru related to its valence state can be measured. The heterometal extended metal atom chain (EMAC) complexes diruthenium nickel dipyridylamide [Ru2Ni(dpa)4Cl2]0,1+ (dpa = dipyridylamide) display the Raman νRu–Ru,str at 327 (broad) and 333 cm–1 in solid form for the neutral and oxidized complexes, respectively, but red-shift to 312 cm–1 on gold NP substrate and to 328 cm–1 on AgNP. According to the oxidation potentials from voltammogram, and the Raman shifts obtained for the model complex Ru2(OAc)4Cl we assign the diruthenium core with charge +5/+4 and +6, respectively for the neutral and oxidized diruthenium nickel dipyridylamide in solid form. On substrate AuNP ...